feat: add race cover image extraction

frontend/src/api/races.ts

@@ -23,6 +23,7 @@ function normalizeRace(input: unknown): Race {
       race?.status === "registered" ||
       race?.status === "completed") &&
     isNullableString(race?.officialUrl) &&
+    isNullableString(race?.coverImageUrl) &&
     isNullableString(race?.startTime) &&
     isNullableString(race?.clusterSchedule) &&
     isNullableString(race?.bibPickup) &&
@@ -48,6 +49,7 @@ function normalizeRace(input: unknown): Race {
     distanceKm: race.distanceKm,
     status: race.status,
     officialUrl: race.officialUrl,
+    coverImageUrl: race.coverImageUrl,
     startTime: race.startTime,
     clusterSchedule: race.clusterSchedule,
     bibPickup: race.bibPickup,